2003 cummins has a rough idle and loaps, sounds like and feels and sounds like a high power cam when in park and warm.. but in gear its perfect or if the air conitioning is on its fine turn a/c off bad loap.. i have 140000 miles had new lift pump, new injectors.and injector pump put in at 98000.when i had bad idle before..its back ..two factory places have ran checks they say everything is fine cant find problem..its costing alot of money to find this problem. it runs great and has plenty of power just rough idle in park

 

i would check all you fuel line connections, crossover tubes and stuff like that...might be suckin some air somewhere

 

maybe the fca could be messed up

 

mine did the same thing, turned out to be a bad injector

 

i think its an injector myself.. they dont last very long.. bummer.. and the money to fix is crazy....also i will check for fuel lines sucking air...what is fca???? thanks for the imput:

 

Fuel Control Actuator. It's attached to the fuel pump.

 

thank you .. man this web site is the bomb.. love it... what is so wierd about the rough idle is i drive it im in gear its fine .. i stop to pick up kids.its in park..rough idle 10 mins later its out there as smooth as could be..soon as i give it fuel ..back to the same thing..and sometimes it will smooth out again in park after about 10 mins.